U.S. patent application number 14/114837 was filed with the patent office on 2014-03-27 for coated active material and lithium solid state battery.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Satoshi Yoshida. Invention is credited to Satoshi Yoshida.
Application Number | 20140087270 14/114837 |
Document ID | / |
Family ID | 47216800 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140087270 |
Kind Code |
A1 |
Yoshida; Satoshi |
March 27, 2014 |
COATED ACTIVE MATERIAL AND LITHIUM SOLID STATE BATTERY
Abstract
The problem of the present invention is to provide a coated
active material having a soft coating layer and capable of
improving a contact area. The present invention solves the
above-mentioned problem by providing a coated active material
comprising a cathode active material and a coating layer for
coating the above-mentioned cathode active material, containing an
Li ion conductive oxide, wherein the above-mentioned coating layer
further contains lithium carbonate.
Inventors: |
Yoshida; Satoshi;
(Susono-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yoshida; Satoshi |
Susono-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Aichi
JP
|
Family ID: |
47216800 |
Appl. No.: |
14/114837 |
Filed: |
May 26, 2011 |
PCT Filed: |
May 26, 2011 |
PCT NO: |
PCT/JP2011/062121 |
371 Date: |
October 30, 2013 |
Current U.S.
Class: |
429/304 ;
429/231.5; 429/231.8 |
Current CPC
Class: |
H01M 4/62 20130101; H01M
4/366 20130101; Y02T 10/70 20130101; H01M 4/5825 20130101; H01M
10/0562 20130101; Y02E 60/10 20130101; H01M 4/505 20130101; H01M
4/131 20130101; H01M 10/052 20130101; H01M 4/38 20130101; H01M
4/525 20130101; H01M 4/485 20130101 |
Class at
Publication: |
429/304 ;
429/231.8; 429/231.5 |
International
Class: |
H01M 4/38 20060101
H01M004/38; H01M 4/485 20060101 H01M004/485 |
Claims
1. A coated active material comprising a cathode active material
and a coating layer for coating the cathode active material,
containing an Li ion conductive oxide, wherein the coating layer
further contains lithium carbonate.
2. The coated active material according to claim 1, wherein a
content of the lithium carbonate is within a range of 0.02% by
weight to 1% by weight with respect to the coated active
material.
3. The coated active material according to claim 1, wherein the Li
ion conductive oxide is at least one of
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 and LiNbO.sub.3.
4. The coated active material according to claim 1, wherein the
cathode active material is an oxide cathode active material.
5. A lithium solid state battery comprising a cathode active
material layer containing a cathode active material, an anode
active material layer containing an anode active material, and a
solid electrolyte layer formed between the cathode active material
layer and the anode active material layer; wherein the cathode
active material is the coated active material according to claim
1.
6. The lithium solid state battery according to claim 5, wherein
the coated active material contacts with a sulfide solid
electrolyte material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a coated active material
comprising a soft coating layer and capable of improving a contact
area.
BACKGROUND ART
[0002] In accordance with a rapid spread of information relevant
apparatuses and communication apparatuses such as a personal
computer, a video camera and a portable telephone in recent years,
the development of a battery to be utilized as a power source
thereof has been emphasized. The development of a high-output and
high-capacity battery for an electric automobile or a hybrid
automobile has been advanced also in the automobile industry. A
lithium battery has been presently noticed from the viewpoint of a
high energy density among various kinds of batteries.
[0003] Liquid electrolyte containing a flammable organic solvent is
used for a presently commercialized lithium battery, so that the
installation of a safety device for restraining temperature rise
during a short circuit and the improvement in structure and
material for preventing the short circuit are necessary therefor.
On the contrary, a lithium battery all-solidified by replacing the
liquid electrolyte with a solid electrolyte layer is conceived to
intend the simplification of the safety device and be excellent in
production cost and productivity for the reason that the flammable
organic solvent is not used in the battery.
[0004] In the field of such an all solid state battery, the
intention of improving the performance of the all solid state
battery has been conventionally attempted while noticing an
interface between a cathode active material and a solid electrolyte
material. For example, in Patent Literature 1, the all solid state
battery such that a reaction inhibition unit having a polyanion
structure (such as borate and silicate) including a central element
(such as B and Si) with an electronegativity of 1.74 or more, which
covalently bonds to plural oxygen elements, is formed at the
interface between a cathode active material and a solid electrolyte
material is disclosed. This is such that the formation of the
reaction inhibition unit having a polyanion structure with high
electrochemical stability at the interface between a cathode active
material and a solid electrolyte material inhibits interface
resistance between a cathode active material and a solid
electrolyte material from increasing with time to intend higher
durability of the battery.
[0005] On the other hand, in Patent Literature 2, it is disclosed
that the cathode active material surface of an all solid lithium
battery is coated with a lithium ion conductive oxide to inhibit a
high resistance layer from being formed at an interface between the
cathode active material and a sulfide solid electrolyte.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Patent Application Publication
(JP-A) No. 2010-135090 [0007] Patent Literature 2: WO
2007/004590
SUMMARY OF INVENTION
Technical Problem
[0008] For example, the increase of interface resistance between a
cathode active material and a solid electrolyte material is caused
for the reason that both of them react to form a high resistance
layer at the interface. As described in Patent Literature 1, the
intervention of borate and silicate between a cathode active
material and a solid electrolyte material allows a reaction between
a cathode active material and a solid electrolyte material to be
inhibited. However, in a coated active material such that a cathode
active material is coated with a coating layer, in the case of
using borate and silicate for the coating layer, the problem arises
that the coating layer hardens. The hard coating layer decreases a
contact point of one coated active material with another or a
coated active material with a solid electrolyte material to bring a
possibility of increasing reaction resistance. The present
invention has been made in view of the above-mentioned problem, and
the main object thereof is to provide a coated active material
comprising a soft coating layer and capable of improving a contact
area.
Solution to Problem
[0009] In order to solve the above-mentioned problem, the present
invention provides a coated active material comprising a cathode
active material and a coating layer for coating the above-mentioned
cathode active material, containing an Li ion conductive oxide,
wherein the above-mentioned coating layer further contains lithium
carbonate.
[0010] According to the present invention, the inclusion of lithium
carbonate in the coating layer allows the coating layer to be
softened. As a result, a contact area of one coated active material
with another or a coated active material with a solid electrolyte
material increases to allow reaction resistance to be
inhibited.
[0011] In the above-mentioned invention, the content of the
above-mentioned lithium carbonate is preferably within a range of
0.02% by weight to 1% by weight with respect to the above-mentioned
coated active material. The reason therefor is to allow reaction
resistance to be further inhibited.
[0012] In the above-mentioned invention, the above-mentioned Li ion
conductive oxide is preferably at least one of
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 and LiNbO.sub.3. The reason
therefor is to allow interface resistance between a cathode active
material and a solid electrolyte material to be effectively
inhibited from increasing.
[0013] In the above-mentioned invention, the above-mentioned
cathode active material is preferably an oxide cathode active
material. The reason therefor is to allow the high-capacity cathode
active material.
[0014] Also, the present invention provides a lithium solid state
battery comprising a cathode active material layer containing a
cathode active material, an anode active material layer containing
an anode active material, and a solid electrolyte layer formed
between the above-mentioned cathode active material layer and the
above-mentioned anode active material layer, wherein the
above-mentioned cathode active material is the above-mentioned
coated active material.
[0015] According to the present invention, the use of the
above-mentioned coated active material allows the lithium solid
state battery in which reaction resistance decreases.
[0016] In the above-mentioned invention, the above-mentioned coated
active material preferably contacts with a sulfide solid
electrolyte material. The reason therefor is that the sulfide solid
electrolyte material is high in reactivity with the cathode active
material, but the use of the coated active material allows
interface resistance between the cathode active material and the
sulfide solid electrolyte material to be effectively inhibited from
increasing.
Advantageous Effects of Invention
[0017] The present invention produces the effect such as to allow a
coated active material comprising a soft coating layer and capable
of improving a contact area.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic cross-sectional view showing an
example of a coated active material of the present invention.
[0019] FIG. 2 is a schematic cross-sectional view showing an
example of a power generating element of a lithium solid state
battery of the present invention.
[0020] FIG. 3 is a graph showing a relation between reaction
resistance and lithium carbonate amount of a lithium solid state
battery obtained in Examples 1 to 8 and Comparative Example 1.
DESCRIPTION OF EMBODIMENTS
[0021] A coated active material and a lithium solid state battery
of the present invention are hereinafter described in detail.
[0022] A. Coated Active Material
[0023] First, a coated active material of the present invention is
described. The coated active material of the present invention is a
coated active material comprising a cathode active material and a
coating layer for coating the above-mentioned cathode active
material, containing an Li ion conductive oxide, wherein the
above-mentioned coating layer further contains lithium
carbonate.
[0024] According to the present invention, the inclusion of lithium
carbonate in the coating layer allows the coated active material
comprising a soft coating layer. As a result, a contact area of one
coated active material with another or a coated active material
with a solid electrolyte material increases to allow reaction
resistance to be inhibited. Li ion conductive oxides such as
phosphate, borate and lithium niobate have been conventionally used
as a material for the coating layer; however, the coating layer
hardens, so that the above-mentioned contact area decreases and
reaction resistance is high. On the contrary, in the present
invention, the use of lithium carbonate as a softer carbonate than
the Li ion conductive oxides allows the coating layer to be
softened. Also, in the coated active material of the present
invention, the cathode active material is coated with the coating
layer containing an Li ion conductive oxide, so that a reaction
between the cathode active material and the solid electrolyte
material may be inhibited and interface resistance therebetween may
be inhibited from increasing.
[0025] FIG. 1 is a schematic cross-sectional view showing an
example of the coated active material of the present invention. A
coated active material 10 shown in FIG. 1 comprises a cathode
active material 1 and a coating layer 2 for coating the cathode
active material 1, containing an Li ion conductive oxide. The
present invention is greatly characterized in that the coating
layer 2 further contains lithium carbonate.
[0026] The coated active material of the present invention is
hereinafter described in each constitution.
[0027] 1. Cathode Active Material
[0028] First, the cathode active material in the present invention
is described. The cathode active material in the present invention
has the function of occluding and releasing Li ions.
[0029] The cathode active material in the present invention is not
particularly limited but examples thereof include an oxide cathode
active material. The reason therefor is to allow the high-capacity
cathode active material. Examples of the oxide cathode active
material used for the present invention include an oxide cathode
active material represented by a general formula
Li.sub.xM.sub.yO.sub.z (M is a transition metallic element, x=0.02
to 2.2, y=1 to 2 and z=1.4 to 4). In the above-mentioned general
formula, M is preferably at least one kind selected from the group
consisting of Co, Mn, Ni, V and Fe, and more preferably at least
one kind selected from the group consisting of Co, Ni and Mn.
Specific examples of such an oxide cathode active material include
rock salt bed type cathode active materials such as LiCoO.sub.2,
LiMnO.sub.2, LiNiO.sub.2, LiVO.sub.2 and
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2, and spinel type cathode
active materials such as LiMn.sub.2O.sub.4 and Li
(Ni.sub.0.5Mn.sub.1.5)O.sub.4. Also, examples of the oxide cathode
active material except the above-mentioned general formula of
Li.sub.xM.sub.yO.sub.z include olivine type cathode active
materials such as LiFePO.sub.4 and LiMnPO.sub.4, and Si-containing
cathode active materials such as Li.sub.2FeSiO.sub.4 and
Li.sub.2MnSiO.sub.4.
[0030] Examples of the shape of the cathode active material include
a particulate shape, and preferably a perfectly spherical shape or
an elliptically spherical shape, above all. Also, in the case where
the cathode active material is in a particulate shape, the average
particle diameter thereof (D.sub.50) is, for example, preferably
within a range of 0.1 .mu.m to 50 .mu.m.
[0031] 2. Coating Layer
[0032] Next, the coating layer in the present invention is
described. The coating layer in the present invention coats the
above-mentioned active material, and contains an Li ion conductive
oxide. Also, the above-mentioned coating layer further contains
lithium carbonate.
[0033] In the present invention, the inclusion of lithium carbonate
(Li.sub.2CO.sub.3) in the coating layer allows a soft coating
layer. The reason therefor is conceived to be that lithium
carbonate is a carbonate and soft as compared with an Li ion
conductive oxide. The content of lithium carbonate in the present
invention is not particularly limited if the content allows the
coating layer to be softened, but is, for example, preferably 0.02%
by weight or more, more preferably 0.1% by weight or more, and far
more preferably 0.3% by weight or more with respect to the coated
active material. The reason therefor is that too small ratio of
lithium carbonate brings a possibility of not sufficiently allowing
the coating layer to be softened. On the other hand, the content of
lithium carbonate in the present invention is, for example,
preferably 3% by weight or less, more preferably 1.5% by weight or
less, and far more preferably 1% by weight or less with respect to
the coated active material. The reason therefor is that too large
ratio of lithium carbonate brings a possibility of deteriorating Li
ion conductivity and electron conduction of the coating layer to
increase reaction resistance though lithium carbonate allows the
coating layer to be softened. Incidentally, the content of lithium
carbonate may be determined by fixing the quantity of
CO.sub.3.sup.2- in the coated active material with the use of ion
chromatography, for example.
[0034] The Li ion conductive oxide in the present invention is not
particularly limited if the Li ion conductive oxide may compose the
coating layer, but examples thereof include an Li ion conductive
oxide represented by a general formula Li.sub.xAO.sub.y (therein, A
is at least one selected from the group consisting of B, C, Al, Si,
P, S, Ti, Zr, Nb, Mo, Ta and W, and "x" and "y" are positive
numbers), and specific examples include Li.sub.3BO.sub.3,
LiBO.sub.2, Li.sub.2CO.sub.3, LiAlO.sub.2/Li.sub.4SiO.sub.4,
Li.sub.2SiO.sub.3, Li.sub.3PO.sub.4, Li.sub.2SO.sub.4,
Li.sub.2TiO.sub.3, Li.sub.4Ti.sub.5O.sub.12,
Li.sub.2Ti.sub.2O.sub.5, Li.sub.2ZrO.sub.3, LiNbO.sub.3,
Li.sub.2MoO.sub.4 and Li.sub.2WO.sub.4. Also, the Li ion conductive
oxide may be a composite compound of the Li ion conductive oxide.
Examples of such a composite compound include
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 and
Li.sub.4SiO.sub.4--Li.sub.3PO.sub.4. Above all, in the present
invention, the Li ion conductive oxide is preferably at least one
of Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 and LiNbO.sub.3. The reason
therefor is to allow interface resistance between a cathode active
material and a solid electrolyte material to be effectively
inhibited from increasing.
[0035] The thickness of the coating layer may be a thickness such
as to be capable of inhibiting a cathode active material and a
solid electrolyte material from reacting; for example, preferably
within a range of 0.1 nm to 100 nm, and more preferably within a
range of 1 nm to 20 nm. The reason therefor is that too thin
coating layer brings a possibility that a cathode active material
and a solid electrolyte material react, while too thick coating
layer brings a possibility that Li ion conductivity and electron
conduction deteriorate. Incidentally, examples of a measuring
method for the thickness of the coating layer include a
transmission electron microscope (TEM). Also, the coverage factor
of the coating layer on the cathode active material surface is
preferably high from the viewpoint of inhibiting interface
resistance from increasing; specifically, preferably 50% or more,
and more preferably 80% or more. Also, the coating layer may coat
the whole surface of the cathode active material. Incidentally,
examples of a measuring method for the coverage factor of the
coating layer include a transmission electron microscope (TEM) and
an X-ray photoelectron spectroscopy (XPS).
[0036] 3. Coated Active Material
[0037] The coated active material of the present invention is
ordinarily used for a lithium solid state battery. The lithium
solid state battery is described in detail in the after-mentioned
"B. Lithium solid state battery". Also, a method for producing the
coated active material is not particularly limited if the method
allows the above-mentioned coated active material, but examples
thereof include a tumbling flow coating method (a sol-gel method),
a mechano-fusion method, a CVD method and a PVD method.
[0038] In a method for producing the coated active material by
using a tumbling flow coating method, for example, in the case
where the Li ion conductive oxide composing the coating layer is
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3, first, a mixed solution in
which Li source, B source and Si source are dissolved in a solvent
is stirred and hydrolyzed to thereby prepare a coating liquid for
forming the coating layer. Next, a cathode active material is
coated with the coating liquid for forming the coating layer by a
tumbling flow coating method. In addition, the cathode active
material whose surface is coated with the coating liquid for
forming the coating layer is burned to thereby form the coating
layer for coating the cathode active material and then obtain the
coated active material. Here, examples of the Li source include Li
salt or Li alkoxide; specifically, lithium acetate (CH.sub.3COOLi)
may be used. Examples of the B source and Si source include a
substance having an OH group at the end or a substance which
hydrolyzes into a hydroxide; specifically, boric acid
(H.sub.3BO.sub.3) and tetraethoxysilane (Si(C.sub.2H.sub.5O).sub.4)
may be used respectively. The solvent is not particularly limited
if the solvent is an organic solvent such as to allow the Li
source, B source and Si source to be dissolved, but examples
thereof include ethanol. Incidentally, the above-mentioned solvent
is preferably an anhydrous solvent. Also, for example, nitrogen
atmosphere is preferable in coating by a tumbling flow coating
method. The reason therefor is to allow the coating liquid for
forming the coating layer and moisture and carbon dioxide in the
air to be inhibited from reacting.
[0039] The hydrolysis temperature is, for example, preferably
within a range of 5.degree. C. to 40.degree. C. Also, the
hydrolysis time (stirring time) is, for example, preferably within
a range of 1 hour to 72 hours.
[0040] On the other hand, the burning temperature is, for example,
preferably within a range of 250.degree. C. to 500.degree. C. Also,
the burning time is, for example, preferably within a range of 0.5
hour to 12 hours. Also, the burning atmosphere is preferably in the
presence of oxygen and specific examples thereof include an air
atmosphere and a pure oxygen atmosphere. Also, examples of the
burning method include a method by using a burning furnace such as
a muffle furnace.
[0041] With regard to the coated active material of the present
invention, the coating layer contains lithium carbonate. A method
for making the coating layer contain lithium carbonate is such that
lithium carbonate may be synthesized by adding the Li source (such
as lithium acetate and ethoxylithium) more excessively than
stoichiometric composition ratio of an intended Li ion conductive
oxide to oxidize the Li source remaining in a reaction with the B
source and Si source. Also, lithium carbonate may be contained by a
reaction between the coating liquid for forming the coating layer
and moisture and carbon dioxide in the air in coating the cathode
active material with the coating liquid for forming the coating
layer. Also, lithium carbonate may be intentionally added to the Li
ion conductive oxide.
[0042] B. Lithium Solid State Battery
[0043] Next, a lithium solid state battery of the present invention
is described. The lithium solid state battery of the present
invention is a lithium solid state battery comprising a cathode
active material layer containing a cathode active material, an
anode active material layer containing an anode active material,
and a solid electrolyte layer formed between the above-mentioned
cathode active material layer and the above-mentioned anode active
material layer, wherein the above-mentioned cathode active material
is the above-mentioned coated active material.
[0044] According to the present invention, the use of the
above-mentioned coated active material allows the lithium solid
state battery in which reaction resistance decreases.
[0045] FIG. 2 is a schematic cross-sectional view showing an
example of a power generating element of the lithium solid state
battery of the present invention. A power generating element 20 of
the lithium solid state battery shown in FIG. 2 comprises a cathode
active material layer 11, an anode active material layer 12, and a
solid electrolyte layer 13 formed between the cathode active
material layer 11 and the anode active material layer 12. In
addition, the cathode active material layer 11 has a coated active
material 10 provided with a cathode active material 1 and a coating
layer 2, and a solid electrolyte material 3.
[0046] The lithium solid state battery of the present invention is
hereinafter described in each constitution.
[0047] 1. Cathode Active Material Layer
[0048] First, the cathode active material layer in the present
invention is described. The cathode active material layer in the
present invention is a layer containing at least the cathode active
material, and may further contain at least one of a solid
electrolyte material, a conductive material and a binder as
required.
[0049] The cathode active material in the present invention is the
coated active material described in the above-mentioned "A. Coated
active material". The content of the cathode active material in the
cathode active material layer is, for example, preferably within a
range of 10% by weight to 99% by weight, and more preferably within
a range of 20% by weight to 90% by weight. Also, the cathode active
material layer preferably contains a solid electrolyte material.
The reason therefor is to allow Li ion conductivity in the cathode
active material layer to be improved. Incidentally, the solid
electrolyte material contained in the cathode active material layer
is the same as the solid electrolyte material described in the
after-mentioned "3. Solid electrolyte layer". The content of the
solid electrolyte material in the cathode active material layer is,
for example, preferably within a range of 1% by weight to 90% by
weight, and more preferably within a range of 10% by weight to 80%
by weight.
[0050] Also, in the present invention, the above-mentioned coated
active material preferably contacts with a sulfide solid
electrolyte material. The reason therefor is that the sulfide solid
electrolyte material is high in reactivity with the cathode active
material, but the use of the coated active material allows
interface resistance between the cathode active material and the
sulfide solid electrolyte material to be effectively inhibited from
increasing. Also, on the occasion, the cathode active material
supporting the coating layer is preferably an oxide cathode active
material. The reason therefor is that the sulfide solid electrolyte
material and the oxide cathode active material react easily and
this reaction may be inhibited by the coating layer. Examples of an
aspect such that the coated active material and the sulfide solid
electrolyte material contact include an aspect such that the
cathode active material layer contains both the coated active
material and the sulfide solid electrolyte material, and both of
them contact in the cathode active material layer. Also, other
examples of the above-mentioned aspect include an aspect such that
the cathode active material layer contains the coated active
material, the solid electrolyte layer contains the sulfide solid
electrolyte material, and both of them contact at an interface
between the cathode active material layer and the solid electrolyte
layer.
[0051] The cathode active material layer in the present invention
may further contain a conductive material. The addition of the
conductive material allows electrical conductivity of the cathode
active material layer to be improved. Examples of the conductive
material include acetylene black, Ketjen Black and carbon fiber.
Also, the cathode active material layer may further contain a
binder. Examples of the binder include fluorine-containing binders
such as PTFE and PVDF. Also, the thickness of the cathode active
material layer varies with constitutions of an intended lithium
solid state battery, and is preferably within a range of 0.1 .mu.m
to 1000 .mu.m for example.
[0052] 2. Anode Active Material Layer
[0053] Next, the anode active material layer in the present
invention is described. The anode active material layer in the
present invention is a layer containing at least the anode active
material, and may further contain at least one of a solid
electrolyte material, a conductive material and a binder as
required.
[0054] Examples of the anode active material include a metal active
material and a carbon active material. Examples of the metal active
material include Li alloy, In, Al, Si, and Sn. On the other hand,
examples of the carbon active material include graphite such as
mesocarbon microbeads (MCMB) and high orientation property graphite
(HOPG), and amorphous carbon such as hard carbon and soft carbon.
Incidentally, SiC may be also used as the anode active material.
The content of the anode active material in the anode active
material layer is, for example, preferably within a range of 10% by
weight to 99% by weight, and more preferably within a range of 20%
by weight to 90% by weight.
[0055] The anode active material layer preferably contains a solid
electrolyte material. The reason therefor is to allow Li ion
conductivity in the anode active material layer to be improved.
Incidentally, the solid electrolyte material contained in the anode
active material layer is the same as the solid electrolyte material
described in the after-mentioned "3. Solid electrolyte layer". The
content of the solid electrolyte material in the anode active
material layer is, for example, preferably within a range of 1% by
weight to 90% by weight, and more preferably within a range of 10%
by weight to 80% by weight.
[0056] Incidentally, the conductive material and the binder used
for the anode active material layer are the same as the
above-mentioned case in the cathode active material layer. Also,
the thickness of the anode active material layer varies with
constitutions of an intended lithium solid state battery, and is
preferably within a range of 0.1 .mu.m to 1000 .mu.m, for
example.
[0057] 3. Solid Electrolyte Layer
[0058] Next, the solid electrolyte layer in the present invention
is described. The solid electrolyte layer in the present invention
is a layer formed between the cathode active material layer and the
anode active material layer, and a layer containing at least the
solid electrolyte material. The solid electrolyte material is not
particularly limited if the solid electrolyte material has Li ion
conductivity, but examples thereof include a sulfide solid
electrolyte material and an oxide solid electrolyte material, and
preferably a sulfide solid electrolyte material, above all. The
reason therefor is to be high in Li ion conductivity as compared
with the oxide solid electrolyte material. Also, the sulfide solid
electrolyte material is so higher in reactivity than the oxide
solid electrolyte material as to react easily with the cathode
active material and form a high resistive layer easily at an
interface with the cathode active material. On the contrary, in the
present invention, the use of the coated active material allows
interface resistance between the cathode active material and the
sulfide solid electrolyte material to be effectively inhibited from
increasing.
[0059] Examples of the sulfide solid electrolyte material include
Li.sub.2S--P.sub.2S.sub.5, Li.sub.2S--P.sub.2S.sub.5--LiI,
Li.sub.2S--P.sub.2S.sub.5--Li.sub.2O,
Li.sub.2S--P.sub.2S.sub.5--Li.sub.2O--LiI, Li.sub.2S--SiS.sub.2,
Li.sub.2S--SiS.sub.2--LiI, Li.sub.2S--SiS.sub.2--LiBr,
Li.sub.2S--SiS.sub.2--LiCl,
Li.sub.2S--SiS.sub.2--B.sub.2S.sub.3--LiI,
Li.sub.2S--SiS.sub.2--P.sub.2S.sub.5--LiI,
Li.sub.2S--B.sub.2S.sub.3,
Li.sub.2S--P.sub.2S.sub.5--Z.sub.mS.sub.n ("m" and "n" are positive
numbers; Z is any of Ge, Zn and Ga), Li.sub.2S--GeS.sub.2,
Li.sub.2S--SiS.sub.2--Li.sub.3PO.sub.4, and
Li.sub.2S--SiS.sub.2--Li.sub.xMO.sub.y ("x" and "y" are positive
numbers; M is any of P, Si, Ge, B, Al, Ga and In). Incidentally,
the description of the above-mentioned "Li.sub.2S--P.sub.2S.sub.5"
signifies the sulfide solid electrolyte material obtained by using
a raw material composition containing Li.sub.2S and P.sub.2S.sub.5,
and other descriptions signify similarly.
[0060] Also, in the case where the sulfide solid electrolyte
material is obtained by using a raw material composition containing
Li.sub.2S and P.sub.2S.sub.5, the ratio of Li.sub.2S to the total
of Li.sub.2S and P.sub.2S.sub.5 is, for example, preferably within
a range of 70 mol % to 80 mol %, more preferably within a range of
72 mol to 78 mol %, and far more preferably within a range of 74
mol to 76 mol %. The reason therefor is to allow the sulfide solid
electrolyte material having an ortho-composition or a composition
in the neighborhood of it and allow the sulfide solid electrolyte
material with high chemical stability. Here, ortho generally
signifies oxo acid which is the highest in degree of hydration
among oxo acids obtained by hydrating the same oxide. In the
present invention, a crystal composition to which Li.sub.2S is
added most among sulfides is called an ortho-composition.
Li.sub.3PS.sub.4 corresponds to the ortho-composition in the
Li.sub.2S--P.sub.2S.sub.5 system. In the case of an
Li.sub.2S--P.sub.2S.sub.5-based sulfide solid electrolyte material,
the ratio of Li.sub.2S and P.sub.2S.sub.5 such as to allow the
ortho-composition is Li.sub.2S:P.sub.2S.sub.5=75:25 on a molar
basis. Incidentally, also in the case of using Al.sub.2S.sub.3 and
B.sub.2S.sub.3 instead of P.sub.2S.sub.5 in the above-mentioned raw
material composition, the preferable range is the same.
Li.sub.3AlS.sub.3 corresponds to the ortho-composition in the
Li.sub.2S--Al.sub.2S.sub.3 system and Li.sub.3BS.sub.3 corresponds
to the ortho-composition in the Li.sub.2S--B.sub.2S.sub.3
system.
[0061] Also, in the case where the sulfide solid electrolyte
material is obtained by using a raw material composition containing
Li.sub.2S and SiS.sub.2, the ratio of Li.sub.2S to the total of
Li.sub.2S and SiS.sub.2 is, for example, preferably within a range
of 60 mol % to 72 mol %, more preferably within a range of 62 mol
to 70 mol %, and far more preferably within a range of 64 mol % to
68 mol %. The reason therefor is to allow the sulfide solid
electrolyte material having an ortho-composition or a composition
in the neighborhood of it and allow the sulfide solid electrolyte
material with high chemical stability. Li.sub.4SiS.sub.4
corresponds to the ortho-composition in the Li.sub.2S--SiS.sub.2
system. In the case of an Li.sub.2S--SiS.sub.2-based sulfide solid
electrolyte material, the ratio of Li.sub.2S and SiS.sub.2 such as
to allow the ortho-composition is Li.sub.2S:SiS.sub.2=66.6:33.3 on
a molar basis. Incidentally, also in the case of using GeS.sub.2
instead of SiS.sub.2 in the above-mentioned raw material
composition, the preferable range is the same. Li.sub.4GeS.sub.4
corresponds to the ortho-composition in the Li.sub.2S--GeS.sub.2
system.
[0062] Also, in the case where the sulfide solid electrolyte
material is obtained by using a raw material composition containing
LiX (X=Cl, Br and I), the ratio of LiX is, for example, preferably
within a range of 1 mol % to 60 mol %, more preferably within a
range of 5 mol % to 50 mol %, and far more preferably within a
range of 10 mol % to 40 mol %.
[0063] Also, the sulfide solid electrolyte material may be sulfide
glass, crystallized sulfide glass, or a crystalline material (a
material obtained by a solid phase method).
[0064] Examples of the shape of the sulfide solid electrolyte
material in the present invention include a particulate shape,
preferably a perfectly spherical shape or an elliptically spherical
shape, above all. Also, in the case where the above-mentioned
sulfide solid electrolyte material is in a particulate shape, the
average particle diameter thereof (D.sub.50) is not particularly
limited but preferably 40 .mu.m or less, more preferably 20 .mu.m
or less, and far more preferably 10 .mu.m or less. The reason
therefor is to allow easy improvement in filling factor of the
solid electrolyte layer. On the other hand, the above-mentioned
average particle diameter is preferably 0.01 .mu.m or more, and
more preferably 0.1 .mu.m or more. Incidentally, the
above-mentioned average particle diameter may be determined by a
particle size analyzer, for example. Also, Li ion conductivity at
normal temperature of the sulfide solid electrolyte material is,
for example, preferably 1.times.10.sup.-4 S/cm or more, and more
preferably 1.times.10.sup.-3 S/cm or more.
[0065] The content of the solid electrolyte material in the solid
electrolyte layer is, for example, preferably within a range of 10%
by weight to 100% by weight, and more preferably within a range of
50% by weight to 100% by weight. Also, the solid electrolyte layer
may contain a binder. Examples of the binder include
fluorine-containing binders such as PTFE and PVDF. Also, the
thickness of the solid electrolyte layer is not particularly
limited but is, for example, preferably within a range of 0.1 .mu.m
to 1000 .mu.m, and more preferably within a range of 0.1 .mu.m to
300 .mu.m.
[0066] 4. Other Constitutions
[0067] The lithium solid state battery of the present invention
comprises at least the above-mentioned cathode active material
layer, anode active material layer and solid electrolyte layer,
ordinarily further comprising a cathode current collector for
collecting the cathode active material layer and an anode current
collector for collecting the anode active material layer. Examples
of a material for the cathode current collector include SUS,
aluminum, nickel, iron, titanium and carbon. On the other hand,
examples of a material for the anode current collector include SUS,
copper, nickel and carbon. Also, the thickness and shape of the
cathode current collector and the anode current collector are
preferably selected properly in accordance with uses of the lithium
solid state battery and other factors. Also, a battery case of a
general lithium solid state battery may be used for a battery case
used for the present invention. Examples of the battery case
include a battery case made of SUS.
[0068] 5. Lithium Solid State Battery
[0069] The lithium solid state battery of the present invention may
be a primary battery or a secondary battery, and preferably a
secondary battery among them. The reason therefor is to be
repeatedly charged and discharged and be useful as a car-mounted
battery, for example. Examples of the shape of the lithium solid
state battery of the present invention include a coin shape, a
laminate shape, a cylindrical shape and a rectangular shape. Also,
a producing method for the lithium solid state battery of the
present invention is not particularly limited if the method is a
method such as to allow the above-mentioned lithium solid state
battery, but the same method as a producing method for a general
lithium solid state battery may be used.
[0070] Incidentally, the present invention is not limited to the
above-mentioned embodiments. The above-mentioned embodiments are
exemplification, and any is included in the technical scope of the
present invention if it has substantially the same constitution as
the technical idea described in the claim of the present invention
and offers similar operation and effect thereto.
EXAMPLES
[0071] The present invention is described more specifically while
showing examples hereinafter.
Example 1
[0072] (Preparation of Coating Liquid for Forming Coating
Layer)
[0073] Boric acid (H.sub.3BO.sub.3, manufactured by Wako Pure
Chemical Industries, Ltd.) and tetraethoxysilane (Si
(C.sub.2H.sub.5O).sub.4, manufactured by Kojundo Chemical Lab. Co.,
Ltd.) were dissolved in 1800 mL of anhydrous ethanol
(C.sub.2H.sub.5OH, manufactured by Wako Pure Chemical Industries,
Ltd.) so as to become 0.066 mol/L each, and 10.8 g of lithium
acetate (CH.sub.3COOLi, manufactured by Wako Pure Chemical
Industries, Ltd.) was further dissolved and mixed therein. This
mixed solution was stirred at a temperature of 19.degree. C. for 24
hours to thereby obtain a coating liquid for forming a coating
layer.
[0074] (Production of Coated Active Material)
[0075] 1.25 kg of a cathode active material
(LiNi.sub.1/3CO.sub.1/3Mn.sub.1/3O.sub.2) was flown in a tumbling
flow bed coating apparatus (manufactured by Powrex Corp.) to coat
the above-mentioned coating liquid for forming a coating layer on
the surface of the cathode active material under a nitrogen
atmosphere. Thereafter, the cathode active material was burned in
the air at a temperature of 400.degree. C. for 1 hour by using a
muffle furnace to thereby form a coating layer for coating the
cathode active material and then obtain a coated active
material.
[0076] (Synthesis of Solid Electrolyte Material)
[0077] First, lithium sulfide (Li.sub.2S) and phosphorus
pentasulfide (P.sub.2S.sub.5) were used as a starting material.
These powders were weighed in a glove box under an Ar atmosphere
(dew point: -70.degree. C.) so as to become a molar ratio of
Li.sub.2S:P.sub.2S.sub.5=75:25, and mixed by an agate mortar to
obtain a raw material composition. Next, 1 g of the obtained raw
material composition was projected into a 45-ml zirconia pot, and
zirconia ball (.phi.=10 mm, 10 pieces) was further projected
thereinto to hermetically seal the pot completely (Ar atmosphere).
This pot was mounted on a planetary ball milling machine (P7.TM.
manufactured by FRITSCH JAPAN CO., LTD.) to perform mechanical
milling for 40 hours at the number of weighing table revolutions of
370 rpm and then obtain a solid electrolyte material
(75Li.sub.2S--25P.sub.2S.sub.5, sulfide glass).
[0078] (Production of Lithium Solid State Battery)
[0079] First, the above-mentioned coated active material and
75Li.sub.2S--25P.sub.2S.sub.5 were mixed at a weight ratio of 7:3
to obtain a cathode mix. Next, a power generating element 20 of a
lithium solid state battery as shown in the above-mentioned FIG. 2
was produced by using a pressing machine. The above-mentioned
cathode mix, graphite (MF-6.TM., manufactured by Mitsubishi
Chemical Corporation), and 75Li.sub.2S--25P.sub.2S.sub.5 were used
as a material composing a cathode active material layer 11, a
material composing an anode active material layer 12, and a
material composing a solid electrolyte layer 13, respectively. A
lithium solid state battery was produced by using this power
generating element.
Examples 2 to 5
[0080] A lithium solid state battery was produced in the same
manner as Example 1 except for modifying the lithium acetate amount
into 32.3 g, 53.9 g, 75.5 g and 97.0 g in the preparation of the
coating liquid for forming a coating layer.
Example 6
[0081] A lithium solid state battery was produced in the same
manner as Example 1 except for modifying the lithium acetate amount
into 97.0 g in the preparation of the coating liquid for forming a
coating layer and performing lithium carbonate extraction treatment
after burning in the production of the coated active material.
Incidentally, the lithium carbonate extraction treatment was
performed in such a manner that 1 g of the coated active material
was poured into 100 mL of pure water subject to inert gas
replacement, filtered after stirred for 5 minutes, and dried in a
vacuum at a temperature of 80.degree. C.
Example 7
[0082] A lithium solid state battery was produced in the same
manner as Example 1 except for performing the preparation of the
coating liquid for forming a coating layer and the production of
the coated active material in the following manner.
[0083] (Preparation of Coating Liquid for Forming Coating
Layer)
[0084] Pentaethoxyniobium (Nb(C.sub.2H.sub.5O).sub.5, manufactured
by Kojundo Chemical Lab. Co., Ltd.) and ethoxylithium
(Li(C.sub.2H.sub.5O), manufactured by Wako Pure Chemical
Industries, Ltd.) were dissolved and mixed in 500 mL of anhydrous
ethanol (C.sub.2H.sub.5OH, manufactured by Wako Pure Chemical
Industries, Ltd.) so as to become 0.6 mol/L each. This mixed
solution was stirred at a temperature of 25.degree. C. for 3 hours
to thereby obtain a coating liquid for forming a coating layer.
[0085] (Production of Coated Active Material)
[0086] 1 kg of a cathode active material
(LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2) was flown in a tumbling
flow bed coating apparatus (manufactured by Powrex Corp.) to coat
the above-mentioned coating liquid for forming a coating layer on
the surface of the cathode active material under a nitrogen
atmosphere. Thereafter, the cathode active material was burned in
the air at a temperature of 350.degree. C. for 5 hours by using a
muffle furnace to thereby form a coating layer for coating the
cathode active material and then obtain a coated active
material.
Example 8
[0087] A lithium solid state battery was produced in the same
manner as Example 7 except for further dissolving and mixing 69.0 g
of lithium acetate in the preparation of the coating liquid for
forming a coating layer.
Comparative Example 1
[0088] A lithium solid state battery was produced in the same
manner as Example 7 except for further mixing 69.0 g of lithium
acetate in the preparation of the coating liquid for forming a
coating layer and performing lithium carbonate extraction treatment
in the production of the coated active material. Incidentally, the
lithium carbonate extraction treatment is the same as the
above-mentioned contents.
[0089] [Evaluations]
[0090] (Quantitative Determination of Lithium Carbonate)
[0091] Ion chromatography measurement was performed by using the
coated active material produced in Examples 1 to 8 and Comparative
Example 1 to calculate the lithium carbonate amount by fixing the
quantity of CO.sub.3.sup.2-. Incidentally, DX500.TM. manufactured
by Dionex Corporation was used for a measuring apparatus, and the
measurement conditions were such that ICE-AS1 was used for a column
and octanesulfonic acid was used for a carrier liquid (eluant), and
the ion chromatography measurement was performed at room
temperature. The results are shown in Table 1 and FIG. 3.
[0092] (Reaction Resistance Measurement)
[0093] Reaction resistance measurement was performed by using the
lithium solid state battery obtained in Examples 1 to 8 and
Comparative Example 1. The reaction resistance of the battery was
calculated by performing complex impedance measurement after
adjusting electric potential of the lithium solid state battery to
3.7 V. Incidentally, the reaction resistance was calculated from a
diameter of an arc of the impedance curve. The results are shown in
Table 1 and FIG. 3.
TABLE-US-00001 TABLE 1 Reaction Lithium carbonate resistance
Coating layer amount [wt %] [.OMEGA. cm.sup.2] Example 1
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 0.3 109 Example 2
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 0.8 119 Example 3
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 1.1 298 Example 4
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 1.4 382 Example 5
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 2.6 405 Example 6
Li.sub.4SiO.sub.4--Li.sub.3BO.sub.3 0.02 421 Example 7 LiNbO.sub.3
0.5 36 Example 8 LiNbO.sub.3 1.2 223 Comparative LiNbO.sub.3 0 788
Example 1
[0094] As shown in Table 1 and FIG. 3, in Examples 1 to 8, it was
confirmed that lithium carbonate was contained in the coating layer
of the coated active material and the reaction resistance decreased
as compared with Comparative Example 1 in which lithium carbonate
was not contained in the coating layer of the coated active
material. In particular, in Examples 1, 2 and 7, the reaction
resistance decreased remarkably. The reason therefor is conceived
to be that a soft coating layer was obtained because lithium
carbonate was contained in the coating layer. Incidentally, in
Examples 4 and 5, the reaction resistance decreased less; the
reason therefor is conceived to be that Li ion conduction and
electron conduction were inhibited because the content of lithium
carbonate was large though the coating layer was softened by
lithium carbonate. Also, in Example 6, it is conceived that the
reaction resistance decreased because lithium carbonate remained by
a slight amount though the lithium carbonate extraction treatment
was performed.
REFERENCE SIGNS LIST
[0095] 1 . . . cathode active material [0096] 2 . . . coating layer
[0097] 3 . . . solid electrolyte material [0098] 10 . . . coated
active material [0099] 11 . . . cathode active material layer
[0100] 12 . . . anode active material layer [0101] 13 . . . solid
electrolyte layer [0102] 20 . . . power generating element of
lithium solid state battery
* * * * *